Optical-field-controlled photoemission from plasmonic nanoparticles

Abstract

At high intensities, light-matter interactions are controlled by the electric field of the exciting light. For instance, when an intense laser pulse interacts with an atomic gas, individual cycles of the incident electric field ionize gas atoms and steer the resulting attosecond-duration electrical wavepackets 1,2 . Such field-controlled light-matter interactions form the basis of attosecond science and have recently expanded from gases to solid-state nanostructures [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] . Here, we extend these field-controlled interactions to metallic nanoparticles supporting localized surface plasmon resonances. We demonstrate strong-field, carrier-envelope-phase-sensitive photoemission from arrays of tailored metallic nanoparticles, and we show the influence of the nanoparticle geometry and the plasmon resonance on the phase-sensitive response. Additionally, from a technological standpoint, we push strong-field light-matter interactions to the chip scale. We integrate our plasmonic nanoparticles and experimental geometry in compact, microoptoelectronic devices that operate out of vacuum and under ambient conditions.Moving from low to high optical intensity, photoemission goes from photon-driven to field-controlled. Consider illuminating a metallic surface with an infrared femtosecond laser pulse with electric field F(t) = F 0 A(t) cos(ωt + ϕ), where F 0 is the peak field, A(t) is the normalized pulse envelope, ω is the carrier frequency, and ϕ is the carrier-envelope phase (CEP). When the pulse interacts with the metallic surface, electrons are excited out of the metal and into the surrounding vacuum. At typical incident intensities, this photoemission process is photon-driven: emission is dictated by the pulse's photon energy, that is, ω, and photon flux, that is, the pulse's intensity envelope ∝ |F 0 A(t)| 2 . At high intensities, this photoemission process resembles field-controlled tunnelling. The strong electric field of the pulse deflects the binding potential of the metallic surface and drives electron tunnelling through the distorted barrier. This tunnelling occurs over a timescale τ t = √ 2mW F /eF 0 , where W F is the workfunction of the surface, m is the electron mass, and e is its charge 19,20 . With sufficiently strong F 0 , τ t becomes shorter than the characteristic cycle time of the exciting laser light (τ t < τ cyc = 1/ω), and individual cycles of the driving electric field eject subcycle electrical bursts from the metal and steer these ultrafast currents through the surrounding vacuum 6,8 ; in this strongfield regime, photoemission is controlled by the driving optical electric field and, accordingly, by the CEP, ϕ.In recent years, metallic nanotips have emerged as platforms to non-destructively investigate photoemission in the strong-field regime. When a nanotip is illuminated by a femtosecond laser pulse, the incident field is locally enhanced at the apex of the tip. Due primarily to the tip's sharp geometry, the field enhancement is typically <10, and th...

Sub-Cycle Effects in Carrier-Envelope-Phase-Sensitive Photoemission from Plasmonic Nanoparticles

“…electric fields in the hundreds of terahertz regime, can control electron motion around solid-state nanostructures. Most notably, carrier-envelope-phase-sensitive (CEP-sensitive) effects have been observed in photoemission currents from metallic nano-tips [1,2] and, more recently, from metallic nanoparticles [3,4]. Here, we report measurements of CEP-sensitive photoemission from plasmonic nanoparticles driven by few-cycle laser pulses of variable intensity.…”

“…Here, we report measurements of CEP-sensitive photoemission from plasmonic nanoparticles driven by few-cycle laser pulses of variable intensity. As the driving intensity shifts, the CEP-sensitive photocurrent shows antiresonant-like behavior that we explain via a simple, quasistatic tunneling model.Our experimental approach follows earlier work [4] and is illustrated in Fig. 1a.…”

“…We illuminate the nanotriangles with tightly-focused (≈ 5 µm beam diameter) few-cycle laser pulses (≈ 10 fs duration at a center wavelength of 1177 nm). The nanotriangles exhibit a localized surface plasmon resonance (LSPR), and when excited by few-cycle laser pulses, the nanotriangles' LSPR and sharp features result in enhanced local optical fields (prior work has shown a field enhancement of ≈ 30 under identical illumination conditions [4]). With our incident pulse energies of 50-160 pJ, we expect enhanced peak fields of 18-32 V/nm (i.e.…”

Optimized octave-spanning Ti:Sapphire laser oscillator characterized by novel two-dimensional shearing interferometry

“…A better result toward single-optical-cycle pulses is expected for optimized cavities using 1% output coupling. The compressed pulses will be used to study field-controlled, carrier-envelope phase-sensitive photoemission from arrays of tailored metallic nanoparticles [2]. We will provide experimental results and detailed discussions in the presentation.…”

“…For example, Ti:sapphire laser oscillators, capable of generating octave-spanning spectra with potentially close-to-single-cycle waveforms, have been employed as optical flywheels providing a very precise timing reference [1], and to study waveform-sensitive interactions with solid-state nanostructures [2]. Despite the experimental demonstrations of octave-spanning spectra from Ti:sapphire oscillators, the intracavity spatiotemporal pulse dynamics has not been completely understood and optimized, and the pulse characterization still remains challenging.…”